AD-AO" M2 SAN FERNANDO LABS PACOIMA CALIF F/6 13/AINVESTIGATION OF CNTD MECHANISM AND ITS EFFECT ON MICROSTRUCTI*-ETC(U)OCT 80 D 6 SAT N000 978-C-0557

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C1 Aeport Prepared for:

U.S. Naval Air Systems Cousand

* Wahington, D. C.

wE Report Period - 9/20/78 to 9/20/79 SJ N 811

S.S

* T Prepared By :Deepak G. U1hat, Ph.D.Research Engineer

ISAN FERNANDO LBRME

Pacoim, Calif ornia

C ~AW~W"e ift p*ilc welease; &uituio uiadate

T

J IVESTIGATION OF CNTD MECHANISM AND ITS

EFFECT ON MICROSTRUCTURAL PROPERTIES,

CONTRACT NO.- NOO019-78-C-0557

Report Prepared for:,/j)//

U.S. Naval Air Systems Command

Washington, D.C.

Report Period - 9/20/78 to 9/20/79

,, 1 , K/, ,,/ * t' 2 -"/ '/ - / * !: X /

Prepared By :,0teepak G./Bhati Ph.D.Research--Eng4i r

Accession For

NTIS GRA&IDTIC TAB

SAN FERNANDO LABORATORIES Iu t Un c t iO l

J.,-tification

Pacoima, California

ir~t>,. '

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Approved for public release; distribution unlimited

October, 1980.

Dlst : . .. 4,

SECURITY CLASSIFICATION OF THIS PAGE (Wten Dota ;nterOd)a

REPORT DOCUMENTATION PAGE BEFORE COMPLETING FSU O1. REPORT NUMBER 2. GOVT ACCESSION NO. 3. RECIPIENT'S CATALOG NUMBER

4. TITLE (and Subtitle) 5. TYPE OF REPORT & PERIOD COVERED

INVESTIGATION OF THE CNTD MECHANISM AND ITS

EFFECT ON THE MICROSTRUCTURE AND PROPERTIES 9/20/78 to 9/20/79

OF SILICON NITRIDE. S. PERFORMING OG. REPORT NUMBER

7. AUTHOR(a) 6. CONTRACT OR GRANT NUMBER(O)

D.G. Bhat N00019-78-C-0557Research Engineer

9. PERFORMING ORGANIZATION NAME AND ADDRESS 10. PROGRAM ELEMENT. PROJECT. TASK

AREA & WORK UNIT NUMBERS

San Fernando Laboratories - "

10258 Norris Ave.Patinma CA Q1 31

I1. CONTROLLING OFFICE NAME AND ADDRESS 12. REPORT DATE

NAVAL AIR SYSTEMS COMMAND October, 1980

Washington, D.C. 20361 13. NUMBER OF PAGES

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Van Nuys, California 91408 SCHEDULE

IS. DISTRIBUTION STATEMENT (of this Report)

17. DISTRIBUTION STATEMENT (of the abstract entered in Block 20, iI different from Report)

1. SUPPLEMENTARY NOTES

IS. KEY WORDS (Continue on revere side if necessary and identify by block number)

Silicon NitrideChemical Vapor DepositionCVDGrain Refinement

20. ABSTRACT (Continue an reverse aide If necessary and identify by block number)

-- This report presents results of a research program in which we sought todevelop a chemical vapor deposition (CVD) method for the deposition ofextremely fine grained silicon nitride.

The program consisted of three separate technical efforts. The firsteffort, a parametric study of the conventional silicon tetrahalide- moniaCVD chemistry, produced no significant grain refinement in the Si3N4 deposits..

D Or 1473 EDITION OF I NOV 65 IS OBSOLETE

SECURITY CLASSIFICATION OF THIS PAGE (WMen Dese &ntNe)

sacuIiTy CLASSIFICATION OF THIS PAG[(Wlhm Daa fntede)

-The second effort attempted, with no success, to utilize silicon halidedisproportionation chemistr the CVD process. Finally, we observedan apparently successful S13NV 4 grain refinement during the third effortin which we used the competing codeposition of separate phases to interruptgrain growth. During this effort, we tried the codeposition of siliconnitride and silicon carbide with no success. However, we found apparentlygood results when silicon nitride was codeposited with aluminum nitride. /

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TABLE OF CONTENTS PAGE

ACKNOWLEDGEMENTS i

LIST OF FIGURES ii

LIST OF TABLES iv

I INTRODUCTION 1

II EXPERIMENTAL PROCEDURE 3

(a) Deposition of Si 3 N4 3

1. Parametric Study 3

2. Silicon Deposition by Disproportionation of a Subhalide 6

3. "Alloying" of Si3N4 for Grain Refinement 8

4. Deposition of Test Bars 11

(b) Evaluation of Si3N4 Deposits 11

1. Transverse Rupture Strength (TRS) Measurements 11

2. X-Ray Diffraction (XRD) 12

3. Scanning Electron Microscopy (SEM) and Energy DispersiveAnalysis of X-rays (EDAX) 12

4. Electron Probe Microanalysis (EPMA) 13

5. Hardness and Fracture Toughness 13

6. Electrical Properties 13

III. RESULTS AND DISCUSSION 15

(a) Parametric Study 15

(b) Silicon Deposition by Disproportionation of a Subhalide 28

(c) "Alloying" of Si3N4 for Grain Refinement 40

(d) Deposition of Si3N4 on Bend Bar Specimens 51

(e) Measurement of Electrical Properties 57

IV. SUMMARY AND CONCLUSIONS 58

References 61

Appendix I: Deposition Conditions for Si3N4 63

Appendix II: Calculation of Transverse Rupture Strength of a 70Coated Beam.

ACKNOWLEDGEMENTS

The work reported here was performed under Contract

#NO0019-78-C-0557 for the Department of the Navy, Naval

Air Systems Command, Washington, D.C.

The author is grateful to Robert A. Holzl, President,

San Fernando Laboratories for the initial guidance of the

research, encouragement and numerous valuable discussions.

Thanks are also due to Drs. Jacob Stiglich and Rodney M. Panos

for valuable discussions and suggestions. The deposition

work was performed by Messrs. Sam Rustomji, Gerald Galarneau,

Clifford Lewis and Philip Kalkowski under the expert super-

vision of Benjamin Tilley. Ms. Colleen Murphy assisted in

the compilation of experimental data.

i

LIST OF FIGURESPAGE

1. Schematic of Deposition Chamber for Silicon Nitride 5Deposition in a Furnace.

2. Schematic of Deposition Chamber for Silicon Halide 7Disproportionation study.

3. Schematic of Deposition Chamber for Aluminum 10"Dopant" Study.

4. Morphology of Si3N4 Made with Nitrogen as the 19

carrier gas.

5. Various crystal morphologies of Si3N4 with Argon 22as the Diluent Gas.

6. Morphology of Si3N4 made with SiF 4 as Silicon Source. 27

7. Free Energy of Formation as a Function of Temperature 30for Various Reactions.

8. Equilibrium Degree of Completion of SiCl4 Reduction 31as a Function of Temperature, Pressure and Degree ofDilution.

9. Equilibrium Degree of Completion of SiHCl Reduction as 32a Function of Temperature, Pressure and DRgree of Dilution.

10. Morphology of Deposit Made in the Silicon Halide 37Disproportionation Study with SiCl4.

A) 500/2500X

B) 600/3000X

11. Morphology of Deposit Made in the Silicon Halide 39Disproportionation Study with SiHCl 3.

A) 70X

B) 200X/1O00X

12. Morphology of Si3N4 Made with Additions of Propane 41to the gas stream.

A) 1000X/5000X

B) 1000X

ii

LIST OF FIGURES (Continued)

PAGE

13. Morphology of Si3N4 made with Methyltrichlorosilane 44and ammonia.

A) AGPP = 0.61 torr 200X/10OOX

B) AGPP = 1.7 torr 200X/O00OX

14. Morphology of Si3N4 made (A) Without and (B) with 49Al addition.

15. X-ray Elemental Density Maps for the Sample in 50Figure 14(b) Showing the Distribution of (A) Aland (B) Si.

16. Morphology of Si3 N4 Deposited in the Aluminum Dopant 52Study. (A) 2000X (B) 50OX (C) lOOX (D) 1000X

17. Morphology of Si N 4 Deposit on Bend Bar Specimens. 56(A) 2000X (B 2000X

ifi

LIST OF TABLES

PAGE

1. Operating conditions for obtaining microprobe data. 14

2. Summary of results on Si3N4 made with nitrogen as the 17

carrier gas.

3. Summary of results on Si3N4 made with argon as the 21

diluent gas.

4. Summary of results on Si3N 4 made with SiF 4 as the silicon 26

source.

5. Summary of results on deposits made in the study of 36SiC12 disproportionation.

6. Summary of results on Si3N4 made with additions of 42propane.

7. Summary of results on Si3N 4 made with CHjSiCl3 as the 46

silicon source.

8. Summary of results on S13N4 made with aluminum addition. 47

9. Summary of results on Si3N4 deposited on bend bar 55specimens.

10. Dielectric Properties of Si3A4 at room temperature. 60

iv

I. INTRODUCTION

The research and development group at San Fernando Laboratories

has been engaged in an in-depth study of the characteristics of

chemically vapor deposited silicon nitride for the past several years.

A major effort in this regard was sponsored by the Department of

the Navy (NAVAIR). A summary report, covering the activities of the

first year which ended in July, 1978 was written under Contract No.

NO0019-77-C-0557. In the present report, we describe the results

of the development work carried out in thL second yuar of the program

under Contract No. N00019-78-C-0557. This work concluded in

September, 1979.

During the first year of effort, we concentrated on the study of

various process parameters in the SiCl,,/NH 3/H2 system. The objective

was to define the deposition parameters that would result in a fine-

grained, dense deposit of a-Si 3N4 on resistively heated tungsten

filaments. We discovered that the substrate temperature and the

total pressure were the major variables which influenced the morphology

of the deposit. We also found that it was possible to influence the

morphology and grain size of the deposits by controlled additions

of hydrocarbons to the gas stream. The measurements of flexure strength,

hardness and fracture toughness (by the indentation technique 2 ) yielded

average values of 550 MPa (80 ksi), 2500-3500 HV5 0 0 and 3-5 MPaVm'

respectively. Isolated values of strength and fracture toughness of

1000 MPa (145 ksi) and 7 MPaAm' suggested the potential of this material

that could be realized by a better understanding and control of the

~-1-

process parameters. We recommended that the efforts be continued

to achieve this understanding and control, and also to attempt the

deposition of translucent or transparent Si3N4 for possible use in

electro-optical applications.

Thus, the objective of the effort during the second year was to carry

out an extended parametric study of the silicon nitride deposition.

Ultimately, we hoped to apply the technique of controlled nucleation

thermochemical deposition (CNTD)* 3-5 to this material. Essentially,

the CNTD process results in a deposit of extremely fine grain size,

of the order of 500-l00OR, and superior mechanical properties. This

process has been successfully applied to the tungsten-carbon system 3

and silicon carbide. 4-6 Other systems in which limited success was

achieved in the application of CNTD include Ti-B and Zr-B . The

significant success with the CNTD process in the SiC system 6

prompted us to examine the possibility of extending the technique to

the other Si based ceramic systems, such as Si3N4. As mentioned earlier,

the efforts during the second year of the NAVAIR program were, therefore,

directed towards this objective. These efforts are described in the

following pages.

We divided the experimental work into a number of categories. In the

first phase, efforts were made to establish process parameters under

the condititions of indirect heating of the substrates in a furnace.

Several variables were selected for study so as to define a set of

conditions for the optimum deposition of Si3N4 with a given gas mixture.

*Process developed and patented by San Fernando Laboratories, a division

of Dart Industries.

-2-

The second phase of the program was onducted concurrently with

a similar program on the development of silicon carbide under the

auspices of Air Force Office of Scientific Research (AFOSR), This work involved

deposition of elemental silicon by the disproportionation of a lower

halide and subsequently, conversion of silicon to SiC or Si3N4 using

appropriate source.

In the third phase of this program, we attempted to co-deposit SiC

to achieve grain refinement. We also studied the effect of "alloying"

of Si3N4 by other compatible cations such as Al. It was expected that

by setting up competitive reactions, it might be possible to prevent

unilateral, columnar growth of any one specie, thereby effecting

grain refinement. In the final stage of the program, several test bars were

coated with Si3N4 for detailed evaluation of structure and properties.I

II. EXPERIMENTAL PROCEDURE:

(a) Deposition of Si3 N4.

The outline of the experimental effort for the second

year was based primarily on the experience gained during the first

i - years' work. Several goals were defined, as described below.

1. Parametric Study:

The first objective was to change the method of heating

the substrate. During the first year, we used tungsten filaments

which were heated by internal resistance in a "cold-wall" reactor. We

decided to use graphite bend-bar type substrates which would be

heated indirectly in a furnace. The advantages of the latter type

(3)

of arrangement are (i) easier scale up (ii) possibility of depositing

on complex shapes, and (iii) no restrictions with regard to electrical

conductivity. Thus, we modified the design of the reactor chamber to

allow for the indirect heating of graphite substrate. Figure 1 shows

the schematic arrangement of the deposition chamber. The graphite

furnace was heated by induction by coils placed around the quartz

envelope surrounding the furnace. A clamshell-type heater was incorpor-

ated on the upstream side to permit preheating of the gas stream.

This arrangement was used to deposit conventional silicon nitride on

the bend bar substrates, during the initial parametric study.

The parametric study was divided into several sets of experiments. These

were (i) use of nitrogen as the carrier gas for SiC1 4 and NH 3, (ii) use

of argon as the diluent gas with no nitrogren in the gas stream, and

(iii) use of SiF 4 as the source of Si.

In the first set, viz. nitrogen as carrier gas for SiCI4 and NH3 , a

total of 32 runs were made ±n which the effect of various parameters was

studied with respect to the rate of deposition and morphology of the

crystallites deposited. The run conditions are given in Table A-1 of

Appendix I. We examined the nature of Si3N4 deposits as a function of

substrate temperature, total pressure, active gas partial pressure (AGPP),

partial pressure of hydrogen and the throughput velocity of the gases

at a constant ratio of SiCl4 to NH 3 of 0.2 (except run #29, see Table A-1

Appendix I). The active gas partial pressure was calculated according to

the stoichiometric proportion of the two species required to make a mole

-4-

NH3 -Ip- 2

SiC14 + N2Chamber Pressure

QuartzChambers

SpecimensIpacetrs

TouVnccue

SpciecienTI

DEPOSITIO INnAuFRNACE

-5-

of Si3N4 -. For example, in the reaction,

3 SiCl4 + 4 NH3 -, Si3N4 4 12HCl (1)

we need 4 moles of NH3 for every 3 moles of SiCIk to make a mole

of Si3N4 . Thus the active gas concentration was obtained by adding

the volumes of SiCl4 and NH3 in the proportion 3:4. Any excess of

SiC1 or NH3 was treated as such, and not included in the calculation.

In the second set of experiments, argon was used as a diluent gas. The

variables were total pressure, substrate temperature, SiCl4/NH 3 ratio,

AGPP, partial pressure of hydrogen and the throughput velocity. A total

of 15 runs were made. The run conditions are given in Table A-2,

Appendix I.

Another useful source of silicon is SiF4. Several runs were made with

this precursor to study the effect of AGPP on the rate of deposition and

properties of the deposit. The run conditions are summarized in

Table A-3, Appendix I.

2. Silicon deposition by disproportionation of a subhalide:

For the second part of the effort, we used various

methods for the deposition of elemental silicon. The reactor chamber

was modified to accommodate a smaller chamber in which silicon bearing

solid materials could be placed. The arrangement is shown in the

schematic of Figure 2. The graphite pot, placed over the furnace

-6-

I

Hi NH3 SiCl4 + N2/Ar

Graphite Pot

TIC

Quartz

Molbydenum Tube

Graphite Potfor Si3N4 chips

J - S3N4 chips

Graphite Furnace I ction Coils

Specimens

To

Vacuum

S,.--Motor Drive for

Specimen T/C fSpecimen Rotation

FIGURE 2 SCHEMATIC OF DEPOSITION CHAMBER FOR SILICON HALIDE

6-v DISPROPORTIONATION STUDY.

was used to hold semiconductor grade silicon chips or silicon nitride

chips and scrap. The silicon bearing precursor gas was passed over

this material to achieve the formation of a lower halide, which

was subsequently disproportionated over the substrate in the furnace.

The initial experiments involving 12 runs were made under the AFOSR

program. SiCI4 was passed over hot silicon nitride scrap (mostly

RBSN from different sources) and then allowed to enter the furnace

to react with ammonia. These runs were then continued under the

present contract and an additional 34 runs were made. In the last three

runs, SiHC13 was used as the precursor gas in place of SiCl4 . The run

conditions are summarized in Table A-4, Appendix I.

3. "Alloying" of SijN4 for grain refinement:

This phase of the program was aimed at grain refinement

by alloying. In this work, we first examined the effect of adding

propane to the gas stream. The purpose was to study the possibility

of carbonitriding of silicon and thereby attempt grain refinement

in the deposit. Most of the nine runs were carried out at a constant

temperature of 1375°C and a total pressure of 40 torr. The variables

were hydrogen pressure, velocity of gases and amount of propane. In

calculating the hydrogen pressure, the contribution of propane

(4 moles of H,, for each mole of propane) was taken into account. The

method used in calculating the active gas partial pressure is discussed

in the next section. The run conditions are given in Table A-5, Appendix I.

I'1

In an alternative approach to the same goal, four runs were made

with methyltrichlorosilane (MTS) as a source of silicon. Again, the

purpose of this brief set of runs was to examine the possibility of

co-depositing SiC and SijN4, since MTS is used for the deposition of

SiC. We attempted a quick survey of the effect of substrate temperature,

hydrogen pressure and total flow on the nature of the deposit. As

discussed in the next section, the results were not encouraging,

therefore, no further work was done. The run conditions are given

in Table A-6, Appendix I.

We were examining the possibility of refining the grain structure of

AIN by the introduction of Si on a concurrent program for Al

development under the auspices of AFOSR. 13 These experiments gave

encouraging results for AIN. Therefore we attempted to carry out

similar experiments for introducing Al into SiN 4 . While attempting

to effect "alloying" of AIN by Si, we had made a brief attempt to

do the same at the other end, i.e. "alloying" of Si3N4 by Al, These

runs, included in this report (see Table A-7, Appendix I), gave

encouraging results. Therefore, we continued this effort under this

program.

The furnace design for these experiments is shown in Figure 3. The

inner quartz chamber was used for aluminum granules. The chamber was

heated by a clamshell heater placed round the outer quartz envelope.

Aluminum was converted to AlCl by reacting with HC1, and then

introduced into the main gas stream near the furnace below. The deposition

O-9-

4 + H2 +-N Chamber pressure

Quartz chambers

Clamshell heater

-Aluminum granules

Graphite Furnace

3bInduction Coils

Specimens

Motor Drive forSpecimen Rotation

Specimen T/C

FIGURE 3 SCHEMATIC OF DEPOSITION CHAMBER FOR ALUMINUM "DOPANT" STUDY

parameters of these experiments are given in Table A-7, Appendix I.

4. Deposition of test bars:

Several test specimens were made by depositing Si3Nqon

reaction bonded silicon nitride substrates. These samples were submitted

to NAVAIR for evaluation and testing. The deposition conditions for

these bars are shown in Table A-8, Appendix I.

(b) Evaluation of Si3 N 4 deposits.

The deposits of Si3N4 made in the various runs were

characterized by different techniques. We used mechanical testing,

microscopy (optical and SEM), X-ray diffraction and electron microprobe

analysis. A brief description of the apparatus and procedure follows.

1. Transverse Rupture Strength (TRS) measurement

A table model mechanical testing machine made by Comten

Corporation, St. Petersburg, Florida was used. The platen of the

machine was fixed to a screw driven by a motor through a reduction gear

train. The linear displacement rate of the machine platen was

1.27mm/min. Flexure testing was carried out in a three-point config-

uration. The fixture incorporated sintered tungsten carbide loading

pins. The load at failure was displayed on a mechanical force gauge.

We used mechanical force gauges (capacities 0-100 lbs. and 0-250 lbs.)

instead of the hydraulic load cells since the former were more accurate

and precise in the range of fracture loads encountered with deposits on

graphite substrates. The standard test specimens were prepared by

1" -11-

A

depositing Si3N4 on graphite bend bars with dimensions 0.1" x 0.2"

3.0" (nominal). Some RBSN bend bars, 0.125" x 0.25" x 3.0", coated

with Si3N4 were also tested. The method of computation of the strength

is given in Appendix II.

2. X-ray diffraction (XRD):

The crystallographic identification of the deposits was

carried out on a General Electric XRD-5 unit at the University of

Southern California. A nickel-filtered copper Ka radiation was used

in all experiments, along with a 30 diverging slit and a medium

resolution 0.20 receiving slit (Soller). Most of the work was

done on as-deposited specimens, except in the case of very coarse-

grained, rough deposits. These were diamond-ground to a flat finish

using 70 micron grit. We also used some samples in a crushed powder

form by grinding some deposit layers in an agate mortar. The samples

were scanned through 150 to 900 20 and the patterns compared with

those from ASTM card #9-250 of the Powder Diffraction File and with

a computer-generated pattern developed by Gazzara and Reed. 8

3. Scanning Electron Microscopy (SEM) and Energy Dispersive

Analysis of X-rays (EDAX):

The electron microscopy work was performed on the

deposits using an AMR 1200A SEM in our metallurgical laboratory.

In addition, we used a Cambridge Stereoscan S4-10 SEM at the University

of Southern California. The SEM examination was limited to an

observation of as-deposited and fracture surfaces. Etched cross

sections were not examined since we have not found a suitable room

-12-

temperature etchant for pure silicon nitride. A Tracor Northern

EDAX system attached to the Cambridge SEM was used for the analysis

of silicon content of the deposits. This information was semi-quanti-

tative at best since the EDAX method is not amenable to the quantitative

determination of light elements (Z<ll).

4. Electron Probe Microanalysis (EPMA):

This technique provides a means of obtaining a fully

quantitative chemical analysis. Samples from the "alloying" experiments

were subjected to EPMA. The analysis was periormed on an ETEC Rl

SEM equipped with an Autoscan Crystal Spectrometer, at Scanning Electron

Analysis Laboratories, Los Angeles. The operating conditions used are

shown in Table I.

5. Hardness and Fracture Toughness

These properties were determined with the aid of a Leitz

Miniload Microhardness tester using a Vickers diamond indentor. Hardness

was measured at loads ranging from 100 to 500g. The fracture toughness

was calculated from the measurement of the length of cracks generated

by indentation. This technique is described by Evans and Charles. 2

6. Electrical properties

The material made under this program was not used for the

evaluation of electrical properties. However, these measurements were

performed by an outside agency on silicon nitride deposits made under

another program. Since San . rnando Laboratories did not participate

AU -13-

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in the evaluation, the details of the techniques were not available.

The results were, however, made available to us through the courtesy of

Mr. Leggett of Hughes Aircraft Company. These are included in the

following section.

III RESULTS AND DISCUSSION

The study of the relationship between deposition parameters and

the characteristics of the deposit was begun on the basis of some

experience gained in the furnace deposition experiments conducted in

a company funded IR&D program. This work was directed towards the

deposition of high strength silicon nitride in thick sections using

graphite substrates. Using the deposition parameters from this study, we

started our effort in the present program. The results of the

various experiments aimed at refining the grain size of the deposits

are described below. The characterization involved examination of

crystal morphology, deposition rate and mechanical properties such

as hardness and fracture toughness. Several specimens were also

tested for transverse rupture strength. The findings of these evalu-

ations are described in the following:

(a) Parametric study:

This study was initiated with a set of parameters in which

nitrogen was used as the carrier gas. Although thermodynamic

calculations suggest that a reaction between SiC14 and N2 in the

presence of hydrogen should yield Si3N4 in the temperature range 1600-

1700K (AGO - -40 to -50 kcal/mol), experience has shown that this does

not happen.

-15-

Kijiima, et al 3 were able to grow 'LSi 3N4 whiskers in the temperature

range 1675-17750K at 1 atm. total pressure when they maintained

a high nitrogen partial pressure (>0.5 atm.) and using very high purity

gases containing less than 10 ppm oxygen and 0.5 ppm H20. At lower

temperatures polycrystalline or amorphous deposits were obtained. In

our experiments, we used nitrogen principally to adjust the throughput

velocity of the gases. Table 2 gives the values of various deposition

parameters in this set of experiments.

The total chamber pressure was varied between 25 torr and about 60 torr.

The low pressure conditions were achieved by connecting the system to

an aspirator. Thus, minor changes in chamber pressure occurred around

a set value depending upon the barometric pressure and ambient temperature

fluctuations. Then, the experiments may be divided into four sets in

which the chamber pressure was maintained in a given range, e.g. 25-30

torr, 39-42 torr, 45-55 torr and 58-62 torr. Within each set, we

examined the effects of other parameters such as the active gas partial

pressure (AGPP), partial pressure of hydrogen and gas velocity on the

deposition rate. The method of calculation of AGPP was described in the

previous section. The velocity of the gases was corrected for chamber

pressure and substrate temperature. Except for one run, the SiCl4/NH 3

ratio was held constant at 0.2.

When the variation of deposition rate was examined as a function of

other parameters within a given set, we could not find any systematic

correlation. An examination of Table 2 shows that the deposit morphology

also appeared to be unrelated to any given parameter.

-16-

FAbLE 2 Summary of results on SIAN, made With nitrogen as carrier gas

GasTotal P* Velocity SlC,, Deposition K TRS

Run Pressure Substrate ACPP H at TP Ni( j rate tlV 200 3 point0 rorr. Temp. OK Torr. Torr M/S Ratio nem/hr _ 0kt MPaW MPa(ksI) Remarks

1-1 25 1b35 0.53 3.0 23.2 0.2 78 Uniform, fine grained deposit.

1-2 25 1575 0.53 3MC 22.3 0.2 78

1-3 25 1500 0.53 3.0 21.3 0.2 - Fine gralned deposit with -omelarge growth spots - clearcrystal lftes.

1-4 25 1500 1.10 6.3 10.6 0.2 - Cuarser grains than prcvlousrun,, some tendency for

wiisker-ilike growth in fewareas.

1-5 26 1650 0.36 2.1 33.8 0.2 48 Clear, fine grained deposit,some spikes.

I-b 39 1650 0.30 1.7 41.8 0.2 48 As above, but no spikes.

1-7 52 1650 0.30 1.7 41.8 0,2 48 Clear, fine grained deposit.

.1 1-8 52 1650 0.31) [.7 41.8 0.2 66 2750 2.95 Clear crystalline deposit-none spikes - Rs substrate.

i-9 48 1620 0.27 1.7 44.5 0.2 48

1-10 64 1650 0.29 1.6 43.8 0.2 36 2800 2.6 Pine crystals and spikcs,cracks on top. RBSN substrate.

1-11 bO 1680 0.27 1.5 47.4 0.2 18 Fine grained clear deposit.

1-12 66 1725 0.30 1.6 44.4 0.2 60 As above, some green colorationIn the 'rystals.

1-13 25 1635 0.53 3.0 23.2 0.2 66 2770 3.35 85.5 Fine crystallites. come

(12.4) spikes. KIISN obist rate.

1-14 40 1650 0.30 1.7 40.8 0.2 102 2725 4.6 152.0 Fine grained atd clear,

(22.0) tranopcrcet de oSI t.eNhS. R -U5 s ,bitrat.

1-15 52 1700 0.30 1.7 43.1 0.2 96

1-16 55 1650 0.32 1.8 39.5 0.2 24 Poor adhesion to sobstroteno spikes, fine depusitL.

1-17 62 1650 0.36 2.0 35.1 0.2 54 Adhesion Is -ltter,d,rk crystals.

1-18 61 1700 0.36 2.0 36.7 0.2 36 l)irk crystalhine deposit ontop, white crystalline ounrest of the hat.

1-19 58 1750 0.33 1.9 39.8 0.2 72 As above.

1-20 58 1800 0.33 1.9 40.9 0.2 - As above, bottom showspoor adhesion.

]-21 59 1650 0.33 1.9 36.8 0.2 - Very thin deposit with a

fine crystallite size.

1-22 45 1650 1.34 2.0 36.2 0.2 66 As above.

12i 47 1650 0.36 2.0 34.7 0.2 - Clear, thin deposit.

1-24 78 1650 0.64 3.7 39.1 0.2 150

1-25 48 1650 0.45 2.6 34.8 0.2 - Thin deposit, partly crystal-line.

1-29 28 1525 1.314 7.3 22.1 2.9 - Poor adhesion of deposit.

1-35 41 1645 0.33 1.9 47.8 0.2 48 Strong (102) orientation, linedark crystalline deposit. [L)AX:('0.5 w/o Si.

1-36 40 1645 0.33 1.8 49.0 0.2 - Coarse(20-2000m)crystallites

on fine grained (mla) matris.

1-37 42 1645 0.33 6.7 46.6 0.2 90

1-38 40 1645 0.60 3.4 26.1 0.2 60

1-58 47 1650 0.38 24.0 40.9 0.2 36 Dark, medium grain size deposit.

1-59 47 1775 0.38 24.0 44,0 0.2 180 2890 4.1 450(65.2) 10-15 am crystallite size,

some large crystals.EDAX: 61.8w/o Si and 0.1 w/o Ctstrong(322) and (222) orientation.

-17-

A typical chemical vapor deposition system contains several variables

such as total pressure, partial pressures of various gases, gas temp-

erature, gas composition, substrate temperature etc. These parameters

are usually interdependent. In addition, in many systems such as

Si3N4 , there are reactions in the gas phase that are not fully under-

stood. Thus, in our system, it was usually difficult to control

these variables in a perfectly reproducible manner. These difficulties

probably resulted in the range of crystal morphologies described in

Table 2 for seemingly similar deposition conditions.

Secondly, the deposition rates, measured by determining the coating

thickness, were subject to considerable error especially when rough

deposits were obtained. Very often, the deposits did not adhere to

the substrate, and no measurements could be made. However, these

findings pointed out the need for a much better control of process

parameters, especially the gas composition, before any correlation

could be attempted. Experience gained in other programs also suggested

that in a furance deposition process, very often the furnace walls

would also be coated. This would then significantly affect the heat

transfer in the gas stream from one run to the next.

We were successful in making fine grained Si4 Nt. deposits as shown in

Table 2. An example of the crystal morphology is shown in Figure 4.

The size of the crystalliets varied widely, even within a given sample.

For example, the crystallite size in Figure 4a is between 2 and lOim,

while in Figure 4b, it varies from about 10 to ;O0w.m. Mechanical

-18-

I

A

A

FIGURE 4 Morphology of SiN,, madO, with nitrogen as the carrier gas.

A) 2000X

B) 200X

' # -i -19

property evaluation of some of the deposits gave reasonable results.

Hardness values ranged from 2700 to 2800 (HV2 90 ) and fracture toughness

from 2.6-4.6 MPafm. As shown in Table 2, the deposits were usually

oriented, with no particular orientation consistently dominant from

sample to sample. EDAX analysis for Si and Cl contents revealed that the

deposits were probably stoichiometric in silicon. For pure silicon nitride

the stoichiometric proportions of Si and N are 60 w/o and 40 w/o respectively.

Some samples showed the presence of small amount of chlorine. It is

not clear if the presence of chlorine is due to residual, unreacted

silicon halide, and whether chlorine is present at the crystallite

boundaries. Since EDAX cannot detect nitrogen or oxygen, it is not clear

if all the silicon is tied up with nitrogen or whether some SiO 2 may also

be present.

Attempts to correlate deposition rates with process parameters for specimens

made with argon as the diluent gas were also unsuccessful. The various

parameters are shown in Table 3. The pressure was maintained at 25-30 torr

and the velocity of gases was maintained, in one set, at 21-25 m/s. The

variable in this set was the SiCl4 /NH 3 ratio, with AGPP at 1.2 ± 0.1 torr

and hydrogen partial pressure at 6.5-7.5 torr. Again, there was no correlation

possible.

Microscopic evaluation of deposits in this set showed a wide variety of

deposit of morphologies - from highly oriented whiskerlike growth to

fine, equiaxed crystallites. Figure 5 shows an example of the range of

morphologies obtained. Most samples showed a crystal morphology similar

to that in Figure 5a. However, in some areas of the coating in a given

sample, a very fine grained deposit was obtained, as shown

-20-

1AMBLE 3 Summary of results on Si ,N,, made with argon a tile diluent gas

Gas TRSTotal Substrate A P Velocity SiCI. Deposition KV? 3 point

Run Pressure TSmp. GPP H2 at TP N113 rate kg/mm Kc PaS Tort. K Torr. Torr. MiS ratio -mhr (Load) MPa/m (kai) Remarks

1-2b 28 1525 1.10 7.3 22.1 2.9 204 Coarse crystallites.

1-27 25 1525 1.70 6.4 24.7 1.8 126 fine, opaque crystals.

1-28 25 1520 0.88 6.5 24.6 3.6 - Preferential growth of spikes due

to hetrogc lius nucleation on

the matrix of fine crystals.

1-30 28 1525 1.14 7.3 22.1 2.9 - Poor deposit, whisker growth,

white needles- appear amorphous.

1-31 28 1475 1.14 7.3 21.4 2.9 - Mixed amorphous type and

crystalline deposit.

1-32 28 1475 1.30 7.3 21.4 2.75 360 Clear, -oarse crystallites.

1-33 28 1475 1.30 7.3 21.4 2.75 156 Coarse, amber crystallite5which appear transparent.

1-3 28 1425 1.30 7.3 20.6 2.75 102 Clear amorphous deposit.

1-39 67 1650 0.55 3.1 45.5 0.2 126 3210 3.55 Depositon a vertical disc,(200) uniform, fine deposit. Analysis

(FDAX) show. 60.7 w/o Si,0.2 w/o C,

1-40 h7 1645 0.55 1.7 45.4 0.2 126 Mixed crystal size along the

periphery of disc. Range 10-12

.m-shows strong (002) orientationin XRD.

1-41 29 1645 1.35 7.5 86.2 2.75 300 as above

i-4 2 29 1545 1.35 7.5 81.0 275 -

-43 28 1525 0.80 4.4 35.9 2.75 186

1-44 28 1535 0.80 4.4 36.1 2.75 - Strong (222),(322) and (304)orientations. Coarse (2O,.m).rystals otid large plikos. Pooradhes on.

L-45 50 1n25 0.72 4.0 42.8 2.75 102 2930 Coarse (15-20i,m) crystalliteb(100) on fine matrix. Amorphous

white deposit on top. latrlxcrysta!s 0.5-Lm.

i -21-

41

AdA

I 44

a -4

00

in Figure 5b. The average crystal size in this photograph is less

than lum. In one sample, long whiskers of the type shown in Figure 5c

were obtained on support rods. The fine crystal facets on individual

needles suggest the possibility of a very fine grain size. Again, the

lack of correlation of process parameters with deposit characteristics

must be attributed to the difficulties in controlling the reactions in

the chamber.

It is of interest to examine the SiCI4/NH 3 system. The reaction

3SiCl4 + 4NH3 - Si3N4 + 12HCl (1)

shows a change in the standard free energy of formation of 9,136 cal/mol10

at 500K. Thus, the reaction, if it were allowed to occur, would

theoretically be complete at a very low temperature. In reality, however,

the tendency for the reactants is to form an intermediate product,

silicon di-imide, Si(NH) 2 . Nihara and Hiral 11 have suggested the

following sequence of events:

SiCI4 + 6NH 3- Si(NH) 2 + 4 NH4Cl

6{Si(NH)2)n 6115° 42{Si 3 (NH) 3 N2 }n + 2NH 3 (2)

925K 3{Si 2 (NH)N,)n + NH3 1475Y

2Si 3N4 + NH3

-23-

Another mechanism that has been suggested is 12

SiCl4 + NH3 - SiCl 3NH2 + HCl

SiCl3NH2 + SiC 4 Si2NHCI 6 + HCl

or

SiC1 3NH2 + NH3 -* Si(NH2cl) 2 + HCI

These intermediate species undergo further interactions by successive

collisions and form more complex intermediate molecules containing

increasing number of N atoms. In these reactions HC is believed to

be eliminated successively in the vapor phase before the gases reach

the substrate surface where formation of Si3N4 is believed to occur.

Lin 23 , in his mass-spectrometric investigation of the intermediates

in the SiCI4-NH3 system detected the presence of SiNH2 Cl2 ions

and several other ions.

In any case, whatever the mechanism of intermediate reactions, it is

clear that these events occurring in the vapor phase are difficult to

control since they depend on intermolecular collisions. Therefore we

decided to explore the possibility of using SiF 4 as a source of silicon.

While SiC14 and SiF 4 are very similar in chemical nature, their

reactivities are quite different. The most important ions derived

from the first comuination of two reactants are similar in SiCl4-NH 3

and SiF 4-NH3 systems,13 but the successive collision products are

quite different. The higher reactivity of the chloride appears to

-24-

accelerate the formation of intermediate polymeric molecules containing

several NH and NH2 groups while in the fluoride system ions containing

more than one NH2 groups are not observed, 14 Thus, it might be possible

to minimize the vapor phase reactions in the SiF4-NH3 system and achieve

a better control of the deposition process.

The results of experiments made with SiF4 precursor are shown in Table 4.

Again, we encountered problems in correlating deposition parameters

and deposition rates. Some indications were, however, obtained that

the rate increased with substrate temperature but decreased with an

increase in the AGPP, other conditions being identical. Very often,

the measurement of deposition rate was rendered difficult due to non-

uniform coating thickness along the length of the bar. This clearly

suggested the possibility of non-uniform temperature and gas composition

along the axis of the reactor. Another problem which could contribute

to this variation was deposition on the furnace walls.

The mechanical characterization of the deposits was more extensive than

in the previous sets. Hardness values ranged from about 2500 to

3150 (HV500) and the fracture toughness was 3.6-5.0 MPavm4 . The flexure

strength values were between about 80-210 MPa, obtained on bars tested

in an as-deposited conditions. Figure 6 shows a typical deposit made

with SiFi, precursor. In one case a crystalline deposit of an average

size between 5 and 10 microns is obtained (Figure 6a). The formation

of powdery surface layers is shown in Figure 6b. This particulate

matter appeared to be adherent to the matrix surface.

II -25-

S - C, V

- , 0 * A , 4

04 0 C M 0 4

0. C C,..0.,> 0> C. C 0

-c -* - 04 .~. 4t04 O O.

B

(b) Silicon deposition by disproportionation of a subhalide

The experiments described earlier were not successful in

making a CNTD deposit of Si3 N4. The nature of the CNTD process tends

to suggest that an intermediate, polymeric product might be required 5

to achieve the grain refinement. While SiCti, might readily lend itself

to such a reaction, its high reactivity to ammonia makes it difficult

to control the reaction near the substrate surface, rather than in

the gas stream.

Rochow 15 has shown that a reaction between SiC1 4 and H2 may lead

to the formation of an intermediate subhalide with an approximate

composition SiC12 .6 1. This precursor is believed to lead to the

formation of CNTD silicon carbide. '+'5 At this point it became

obvious to us that the conventional CVD system was probably not suitable

for the grain refinement of Si3N,,. We, therefore, sought alternative

approaches to the conventional one. One possibility was to deposit

elemental silicon and then attempt its nitridatlon.

While it may be possible to deposit elemental silicon by a variety

of methods using different precursors, it appeared to be appropriate

to use the same basic system of SiCI. -H2 or SiHCI3 -H,' that we had

extensively used in our investigations of silicon ceramics. Also,

there were potential advantages in depositing silicon by first forming

a subchloride and disproportionating the same over a substrate. The

most obvious potential benefit was grain refiliVmeut if the disproportion-

ation could be carried out simultaneously with nitridation.

-28-

We studied the feasibility of this approach for the following reactions:

SiCl4 (g) + Si(s) 2 SiC12(g) (4)

2SiHCl 3 (g) + Si(s) * 3S1C1 2 (g) + H2 (g) (5)

The lower halide is produced by passing SiC1. or SiHCl 3 over hot

semiconductor grade silicon chips in a graphite crucible. The variation

of the standard free energy change of the reactions with temperature

for the silicon chip crucible is shown in Figure 7.

The equilibrium constant of the reaction, K = exp (-AG/RT), can also

be expressed in terms of composition and total pressure, and, for the

two reactions considered above is given by:

K4 = SiCI2 P (6)n SiCli [ Si C12 + nSCl 4 + n]

SiC 2 . nH2 P 2 (7)K5 =-n----HCI + +

LSiHC14 SiCl 2 +nH 2 +nSiHCl 3 +

Where ni is the number of moles of the ith species, nI is the number

of moles of the inert (carrier) gas(es) and P is the total pressure.

Using these expressions, the equilibrium degree of completion of the

reactions was determined for different values of the parameters n I/nR

and P where n I/n R = the ratio of the moles of inert gas to the moles of

reactant gases, or the degree of dilution of the gases. The results are

plotted in Figure 8 and 9.

-29-

iool

807~

86&-

40-1

-~20-

05

0-

0U-4 H

3-40-

-fRef. #9

-1001 L 1 ~1000 1400 1800 2200

TEMPERATURE, K

1. 3Si(s) + 2N2(g) - Si3N4(s) Ref. #9

2. Si(s) +- N3g S13N,4(S) + 2H2(g)4 1

3. SiC14(g) + 4 NH3(g) - -1 Si3N4(S) + 4HC1(g)

4. 2SiHC13(g) + Si(s) - 3SiC12(g) + H2(g)

5. SiC14(g) + Si(s) -~ 2SiCl2(g)

4 16. SiF4(g) + - Nli3 (g) - 3 Si3N4(S) + 4HF(g)

7. SiCz.(g) + -1S13N4(S) - 2SiC12(g) + 2~ N2(g)

8. SiFi4(g) + H2(g) - SiF 2(g) + 2HF(g)

FIGURE 7 FREE ENERGY OF FORMATION AS A FUNCTION OF

TEMPERATURE FOR VARIOUS REACTIONS.

-30-

0000

N009T0

-44 C-4

-104 E4 0

+4- )009T' w

E-4

Cd~~C F '-4

C.' NOOE T41-

CC,

-31-

II I -T [ l l l

0.0

1 . 0 -... _ ._ ._ .. ,. .. - ........ .

Q. 0.95

//,/ - ni~nR , torr

//7 1 38! / 10 38

A, 1 380A20 380

/1 / 0 1 610iiII20 610

0.90 6 1 760 --44,-4 A 20 760

2 SiHC1 3 (g) + Si(s) i 3 SiC1 2 (g) + H 2 (g)

L!nSo 0 0 0 0

r4 -

0.85I0-I 1 10 102 103 104

FIGURE 9 EQUILIBRIUM DEGREE OF COMPLETION OF SiHC13 REDUCTION AS A FUNCTION

OF TEMPERATURE, PRESSURE AND DEGREE OF DILUTION.

-32-

Considering reaction (4), it is clear that a substantial amount of

SiCI 2 can be generated above 1500°K if the total pressure is reduced

to 40 torr and sufficient dilution of the gas stream is carried out

(Fi&ure 8.) Having achieved the formation of SiC12 in the Si reservoir,

the reaction can then be reversed near the substrate simply by drop-

ping the temperature to form a deposit of silicon, which may then be

carburized or nitrided as the case may be. In this approach, the

purpose is to cause a disproportionation of the lower chloride which is

believed to result in a finer grained deposit of silicon, than would

result from direct reduction of SiCL by hydrogen. Calculations

indicate that the yield of silicon by the latter reaction will not

be significant at 15000K and 40 torr with dilutions up to 20:1.

Similar considerations for reaction (5) involving trichlorosilane

show that the formation of SiCI 2 is very energetic over the

temperature range 1300°K - 17000 K, indicating that SiHCI 3 may

be a more efficient source of SiC1 2.

The use of a silicon reservoir imposes an upper limit of =16750K (M.P.

for silicon) for the reservoir temperature since the presence of

liquid Si would create handling problems in the reactor. This

problem may be circumvented by using Si3N chips instead as the

reducing agent, since it is more stable at these temperatures.

The reaction can then be written as:

-33-

1[2SiC1 2 (g) + 2(gSiCl 4 (g) + - Si 3N4 (s) -- N2 (g)

Figure 7 shows that reaction (8) is feasible only near 20000K

under standard conditions. Figure 8 reveals that this reaction will

proceed to completion at low pressure and high dilution. Once SiC12

is formed via generation in the chip pot, thermochemical data

suggest that it is relatively easy to cause disproportionation and

subsequent nitridation using a suitable source. The reaction for

the formation of Si3N4is:

3SiCI 2 (g) + 4NH 3 (g) - Si3N 4 (s) + 6HC1(g) + 3H2 (g) (9)

This reaction will proceed very energetically even at room temperature.

Alternatively,

2SiCl 2(g) + Si(s) + SiCl 4 (g) (10)

3Si(s) + 4NH3 (g) Si 3 N4 + 6H2 (g) (11)

3SiCl,(g) + 4NH3(g) : Si 3 N4 + 12HCI(g) (1)

Calculations of standard free energy changes show that rfaetiors -01)

and (1) will both occur with nearly equal ease in the range 1500°K-180 0 °K.

-34-

These reactions should also occur favorably with nitrogen instead of

ammonia as the nitriding specie although with much less vigor. Reactions

(11) and (1) may also be carried out at much lower temperatures; however,

one is then concerned with the rate of deposition and morphology of

the deposit.

Several runs were made in this study as shown in Table A-4, Appendix I.

Table 5 summarizes the results of evaluation of the deposits.

The deposition was carried out by passing SiCLf-bearing carrier gas

through the reservoir containing silicon source material (pure 91, or

scrap RBSN). Several experiments were made in which the SiC12 formed

in the reservoir was allowed to mix with ammonia near the substrate.

In other cases, SiC12 was merely allowed to disproportionate to form

silicon. In some experiments the reservoir was empty but was used

as a preheat chamber for SiC14 which subsequently reacted with NH3.

We made several runs at high chamber presures (450-600 torr) to assess

the effect on deposition rate. In these runs, the nitrogen flow rates

were varied from 0 to 10 liters/min. In those runs where no nitrogen

was used, we did not get any deposit although argon was used as the

diluent. Most of the deposits were powdery, loose and difficult to

evaluate. Figure 10a shows the deposit obtained when SiC14 was passed

through an empty silicon reservoir being used merely to heat the gas

to about 19000 K. The deposit has a crystalline morphology with a size

of about 10-15pm. The mechanical properties data suggest that the

-35-

TABLE 5 Results of tests on samples deposited in the study of silicon halide disproportionation

RUN kg/mm2

K TRS.MPaI (Load) MPa- (kei) Remarks

569 White powdery deposit573 1085 (50) Thick powdery gray deposit574 Grey silicon deposit under a layer of yellow

powdery layer.

575 600 124 (18) Fine crystalline Si regions of botryoidal morphology.

576 Powdery yellow deposit.

577 2645 (100) Non uniform deposit. Partly powdery yellow, partlycrystallLne L

_gstlii~ rey deposit.578 1035 (100) Grey, powdery deposit with metallic lustre.

579 3235 (100) Non uniform deposit containing yellow powdery andgrey coherent areas.

580 XRD shows riSi N (some). Non-faceted grey crystallinesurface.

581 1005 Non uniform nitridation, XkD OSL3N,, 4-SiC. Top3401 (500) of bar shows aSiNs. OSiC and Si.

582 XRD q-Sie, c-SiIN4, some .SiC. Dar metallicrovf surface with fine graj d rexrns._

583 A mixture of grey coherent botryoidal deposit and.__ an d y ell ow o wde ry deposit. ____________

585 XRD: a-Si1 3N., SSiN. Mostly powdery deposit. someneedle-like areas. Dissolved in Hf I HNO. - --

586 Coherent, fine grained deposit with some :onicaltopograhy o the top of bar. ____

587 Mixture of fine sod coars- globuler crystallites.columnar crystal habit.

588 XRD: uSi IN,, Slo. Bottom-shiny grev crystals, top,grey powdery de-osit. ___

589 XRD: Graphite, grey powdery deposit - XI(D shows

graphite and some SiN*.

590 XRD: -SiiN, + graphite. tdreenish white powderydeposit.

591 Greyis white powdery deposit.592 3380 (500) XRD: nSiN4 with traces of -SijNu. White soft,

fluffy deposit.

593 Mixed fine-grained and needle-like_dposit.

594 3200 (500) 138 (20) Mixture of coarse and fine faceted cryta~ittes.595 2930 (NC-350 4.15 138 (20) Coarse and fine faceted grains, good adhesion to

3320 (rarrett SN) RBSN substrats. _-----

596 2460 (500) Coarse and finegained crs'stallites.597 2990 (500) 5.8 244 (35.4) Fine grained depoi_.with ,Lor adhe.ion ,

598 Fine needle shaped crystals dispersed in a fine--__ powdery deposit.

599 Fine needle shaped crystals dispersed in a finepowdery deposit.

600 2710 (500) 4.4 143 (208) Dark, powde_ _surface layer ona coherent dark denosit.

601 3270 (500) 3.6 Dark faceted deposit on to resto st. ao TA-602 Loose whisker-like crysta;.jites on a cryst lline deqs.

603 Deposit similar to run I 598 and 599.604 Deposit similar to run I 598 and 599.

605 Mixture of fluffy whisker-like owthn.__ pyery denoos -606 Black crystalline deposit and white fluffy regions. Some

areas show "fused" spots.

"60 7 No deposit.

608 No deposit.

609 No deposit.

610 1150 (100 Matrix of fine grained deposit covered with yellowpowdery layer.

61l 1200 (50) Same as 610.

612 1075 (100) _-Same as 610.

613 Dendritic growth near top, coarse faceted crystallites

and fine rev deposit.614 Transparent loose needle-likeIdeosit.

615 ph whisker-like deposit.

616 .i...... . ..... ............--- -- --- --- ---.... ..... ... .e l .l . ..

,1i 21,90 (.Of)) 3.8 MiXL t. oi d.-like and ic tedo cry sta morpho ....618 Smooth, amorphous looking deposit with some fine

crystalline areas.

FIGURE 10 Morptio I(),, ,g ' Ipitni ill tt ilicon hal ide

disproport i Omm ti'm ,t od. Wit h s ic

A) 'Ofl/2")()OX

B) 600/ 3 ) /

material is CVD Si 3 N4 (See Table 5, run #597.) Figure lOb, on the

other hand shows the structure of sample #610 which was made by passing

SiC14 over CVD Si 3N4 chips but without any ammonia. The deposit

is powdery on a matrix of fine silicon layer. This and other samples

that we could test showed hardness values of HV 1075 to HV 1200, sug-

gesting that the material was probably silicon. Thus, despite the

thermodynamic feasibility of nitridation of silicon,(Figure 7) we did

not succeed in nitriding elemental silicon with nitrogen.

In other experiments where ammonia was used, we could form silicon

nitride. In some cases traces of 6-SiC were found in the XRD patterns.

In one run (#589, see Table 5) where no nitrogen source was used, the

deposit exhibited a B-Si 3N 4 pattern, indicating that the Si3NL4 used as

a silicon source had probably decomposed and redeposited.

In general, the results of disproportionation study were rather disap-

pointing. The three runs made with SiHCI 3 instead of SiC14 resulted

in a silicon nitride deposit which showed a CVD type crystal morphology.

Figure Ila shows the deposit of Si 3N, with a crystalline morphology.

Several large rounded and faceted crystallite are observed on the

matrix of platelets having an average dimension of 50-]0im. Another

sample, shown in Figure llb, appears to have a rounded, botryoidal,

morphology. However, it became obvious that deposition of fine grained

SijN via disproportionation of SiCl, and subsequent nitridation would

be very difficult.

-38-

r__ -7

Ilif

FIUE1-opooyo kpsbtnd nteslcnhld

Aipootin tinsuYw hSl~

A) 7O

B 0X/:o

(c) "Alloying' of SigN, for grain refinement

The idea of introducing a parallel reaction in the gas stream

to curtail the columnar growth of a deposit during chemical vapor depo-

sition is not new. Researchers have effectively used this technique

for example, for the grain refinement of tungsten. 17 '1l In our

experiments we decided to use an essentially similar approach.

During the first year on this program 1 we had examined the feasibility

of using propane for this purpose. In that study, we attempted to

co-deposit SiC and Si3N4 on the resistivety heated tungsten filaments.

Although we could not succeed in doing so, we found that frequently

the presence of propane in the gas stream probably led to a relatively

finer, columnar crystallites. We, therefore, used this approach in

an attempt to reduce the crystallite size of Si3N4 made in a furnace.

The run conditions for these experiments are given in Appendix I,

Table A-5. Table 6 summarizes the results of evaluation of deposits

made with propane additions. Again, no specific trend can be detected

as far as relating deposition rate with process paramenters. For example,

Runs #51 and 55 were made under identical conditions but the deposition

rates were different. XRD showed random orientation of deposit in

one case while the other showed a stronly oriented deposit. Tho

photomicrographs (Figure 12) showed typical, well-faceted deposits

Fi&ure 12a shows the surface topography of sample #50 (Table 6). The

crystallite size is 5-10m. By comparison, sample #56 (Figure 12b)

shows massive crystals, about 30um in size. Table 6 shows that for

sample #56 the active gas concentration (SIC]i, + NH-) is much higher

than for sample #50, and the deposition rate is more than doubled.

-40-

A

B

I FIGURE 12 MorphiolIogy of Si N vniIdt wi th adi(Ition ofl f propane.

to tit he a tlr I

A) I ()()(X / O )UX

1j) I ()t)()x

I-r :

= - ' - .-.

C . . S ..

.. . . .. ..c P. tu. . .n, Zr

a

summarized in Table 7. The samples generally showed poor adhesion to

the substrate, and strong crystal orientation, in XRD. We did not

find any trace of SiC, or carbon in the deposit. The crystallite size

varied considerably, as shown in Figure 13. Comparing Figures 13a and

13b an increase in t,.e active gas concentration may have resulted in

an apparent grain refinement to some extent. However, these experiments

also proved to be unsuccessful in producing fine grained Si4N4 with any

consistency.

We, therefore, decided to terminate these efforts, and attempt co-dep-

osition of AIN. Aluminum nitride is deposited by causing a reaction

between AlCI3 and NH,:

AICI(g) + NH (g) -AIN(s) + 3HCI(g) (14)

The study of this system was being carried out on another program

sponsored by AFOSR.7 We were conducting experiments to refine the

grain structure of CVD AlN by introducing silicon in the gas stream.

A natural extension of this work was to explore the feasibility of this

approach in the system SiNu + Al. Some of these experiments were

carried out under the AFOSR program. Since this work was directly

applicable to the present program, the details of these experiments

are included in this report. Table 8 gives the summary of results

obtained from the samples in this work.

The sample in run #652 was made without any additions of Al and resulted

in a typical CVl) Si Nj, deposit. Two samples from this group were

-43-

BA

FIGURE 13 Morplogy,,v, ') \md r withIio~I n

16 andl nmnon i ,i

(A) A(; IT' ).,I',t (B) A(J 1 1.7 torr

The higher concentration of C3H8 apparently only introduces greater

amount of hydrogen since no carbon or SiC was detected in the XRD

pattern for sample #56. The interrelationships of the various parameters

in this case are interesting but unknown. Thus, in general, the addition

of propane did not appear to have much beneticial effect on the grain

size of the deposit.

We made another attempt to introduce a carbon source to influence the

reaction between Si and N2. Methyltrichlorosilane is an excellent

precursor for the deposition of SiC. 4 The reaction is:

CH.jSiC1 3(g) SiC(s) + 3HCI(g) (12)

We attempted to influence this reaction with the addition of ammonia.

We were interested in the following possible reaction, although other

reactions sequences were probably also feasible.

CH3SiCI3 (g) + A NH3(g)- lSI3N4(s) + HCl(g) + C(s) + 2H2 (g) (13)

Alternatively, it might be possible to combine reactions (12) and

(13) so that co-deposition of SiC and Si3N4 could occur. Calculations

of the change in free energy of the reactions suggested that the

combined reaction would be more favorable than reaction (13) under

standard conditions. If this could be achieved under reduced pressure,

and other parametric constraints, we might be able to utilize the

differences in the reaction rates of formation of SiC and Si-N, to

achieve grain refinement. The results of these experiments are

-45-

IC I

I C -CC~ I.C C

I *~1 2 r 0 52: a-

C' t-j 0

-- a'-"Ic 'C4

ICCA ?~0 I

C' 4 CC

CC CO -Va;C'' I

22-2

'-C YCCI C I CC ' r CC,~a I ~ Zo

7 00 ICr. I

C' Fi 'a C.-'

2li ~- I I.0 N

3C , I

'0 0d

a'- oQ'C~ a; -, a a;CCC' 0 (1 -a a;- C' A - a; a; a;

C a; '"C. I-'C I -~'C CaI..C~ - C'~CC' -.- , - a; -a -CC (3--.-'S -7 -aC' CC

I C

-. -to' - I C' C'

o C..-'

0' ~I'~- a; -~ ' 4 -CC ~

C'a . - -

C. C - -C.C. 12: FC ~ C C

.0 '~ 0 '0a - - -

4 C F

ICC a o a aoat- .7C-'C' I

.4 - ~- C' C'C' 'C'0 ' -a -a*0 § p I

1-' C' - ' C I-46-

1)

[1

TABLE 8 Summary of results on deposits made with Al as "alloying" addition

Substrate Deposition HIV TRS

Run Pressure Temp. Rate kg/rn" K MPa0 Torr

0K wm/hr (Load) MPazm (kai) REMARKS

8-652 65 1600 100 3255 - 376 Non-uniform deposit morphology from(100) (55) top to bottom, from fine crvstallites

to coarse faceted crystals.

8-653 65 1625 2960 - 158 same as above.(200) (23)

8-656 65 1595 - - 290 Glassy deposit with rounded domes

(42) and areas of faceted crystallites.Poor adhesion and integrity.

8-655 65 1590 3410 - Fine grained deposit with rounded(100) domes on the surface.

8-656 65 1590 2560 - 129 Amorphous type deposit with microcracks.(500) (19)

8-657 65 1585 250 2330 4.9 - Translucent deposit with fine grained

(500) domes on the surface.

8-658 90 1595 2320 3.2 - Dark shiny deposit with domes.(200) Fracture surface appears glassy, non-

columnar.

8-659 90 1590 Fine-grained. columnar deposit,

with surface cracks.

8-660 50 1420 Whitish amber deposit on top, dark

at the bottom, appears glassy in

fracture.

8-661 62 1425 same as above.

16-182 73 1750 74 Fine-grained deposit, cracked near

top on graphite substrates.

16-183 73 1750 - Whisker-like growth on the entire

surface.

16-184 72 1750 146 Fine grained, uniform deposit.

16-185 75 1750 174 1945 3.2 204 Botryoidal morphology of deposit,

(29.6) cracks on the surface. Size of rounded

crystallites varies widely (iO-50um).Some porosity in the deposit.

16-186 75 1735

16-187 76 1750 150 Lavered deposit showing a mixture of

dense columnar growth, porous banded

region and preferential growth ofhexagonal platelets on the surface.

Generally columnar, coarse rounded

crystallites. (20-50m)

16-188 76 1750 142

16-189 74 1750 105

16-190 72 1750 - 2170 5.3 225 Faceted crystalline deposit surface

(300) (32.6) with columnar grains. Surface shows

randomly oriented platelets with

edges nearly normal to the surface

of deposit.

i1 16-191 76 1750 194 1890 3.5 168 Finely cracked, botryoidal deposit

(24.4) with size of rounded crvstallites ranging

from 10 to 301m.

16-192 79 1710 149

16-193 91 1750 182 Layered deposit showing columnar,

porous, layered and granular

morphologien in the fracture

cross section.

1!

: -47-

analysed extensively to study the effect of incorporation of Al.

Fi&ure 14a shows a typical CVD Si3N 4 deposit with columnar grain

structure. In comparison, the grain refinement achieved by the

incorporation of Al in the material is clearly visible in Figure 14b.

The distribution of Si and Al in the material is shown in the X-ray

elemental density maps (Figure 15). The complimentary variation of

the concentration of Al and Si is clearly visible. This suggests

that both Al and Si were incorporated simultaneously since the

<4 elemental map for nitrogen showed a uniform distribution in the section.

This result clearly indicated the possibility of refining the grain

structure of Si3N4 by adding Al to the system.

Further work was carried out to select optimum deposition conditions

for the incorporation of Al (Runs #182-193, Table A-7, Appendix I).

In any CVD operation the compatibility of the coefficients of

thermal expansion of the substrate and the coating is an important

consideration. When AlN is incorporated in Si3N4, the value of the

coefficient of thermal expansion, a, of this dual-phase coating is

different from either of the constituents. This presents some

problems in maintaining the integrity of the coating. We addressed

this point by studying the nature of deposits on various graphite

substrates and hot pressed silicon nitride bend bars.

The microscopic evaluation of the coatings revealed that although some

grain refinement could be discerned, there were problems related to

the deposition that were difficult to control. For example, as shown

-48-

A

FIGURE 14 Morphology of SijN, made (A) Without and (B) with Al addition

Magnification 200X

------- --

0o

ai

-4

Ez..

in Figure 16a, we obtained a deposit which was practically free of

distinct columnar grain structure although the surface revealed the

uneven botryoidal topography (Figure 16b). On the other hand, another

sample showed a considerable variation in the fracture topography

(Figure 16c). The initial deposit was columnar, but became progressively

porous. The top layer (about 10pm thick) almost totally delaminated

from the rest of the coating. This layer also had an unusual crystallite

orientation as revealed in Figure 16d. These variations in the

morphology through the coating suggested non-uniformity of the deposition

conditions during the run.

These experiments were successful to the extent that we could demonstrate

the possibility of CNTD-type grain refinement in Si3N4 by incorporating

a suitable second phase. Detailed evaluation of these samples and

further exploration was not carried out due to the constraints of time

and funds. However, there is no doubt that a more thorough exploration

and understanding of these reactions in a systematic manner is warranted

and should be continued.

(d.) Deposition of Si3N4 on bend bar specimens

We made a series of runs in which conventional CVD silicon

nitride was made and deposited on HLM graphite and RBSN substrates.

The purpose of these samples was to evaluate the CVD silicon nitride

made in an indirectly heated furnace and compare the results with

those obtained on tungsten filaments.1 We tested some samples for

strength, hardness, fracture toughness and crystal morphology. Some

-51-

I:I

rg

I

FIGURE 16 Morpho i ogv of Si N dtip)s ite d in the alt minum dopant study.

(A)

C-- - .. .

'

FIGURE 16 Morphology of Si dN d 'pOsitLd in thc aluminim dopant study.

(C) 1000X

(I)) lO5OX

-53

b'i''~ . . . .. .. I I - " I I .. . 1 7 I I

samples were sent to Mr. R. Rice of Naval Research Laboratory for eva]-

uation. The results of our tests are summarized in Table 9.

Figure 17 shows the morphology of a typical deposit in this set.

Usually, the attempts to obtain fine-grained deposits on resistance-

heated filaments resulted in amorphous or glassy morphologies. The

mechanical properties of samples in the present work were comparable to1

those in the earlier work.

The fracture energy tests carried out at Naval Research Laboratory

showed 19 that the CVD Si 3N4 made at San Fernando Laboratories

exhibited a fracture energy of about 20 J/m2 , comparable to values

obtained on materials from other sources. The calculations of fracture

energy on the basis of indentation fracture toughness measurements that

we carried out gave values in the range 17 to 86 J/m 2 with an average

of about 40 J/m2 . The difference probably reflects the relative sample

size in the two types of tests. There is another possibility for

the difference in the fracture energy values. The samples for

indentation fracture toughness measurement are polished ceramographically.

This procedure usually introduces a residual compressive stress on the

surface. We did not anneal the samples after polishing to remove any

possible residual stress. In addition, the error in the measurement of

crack length using the microhardness tester at 400X probably resulted

in an over-estimation of the fracture toughness by this technique of

about 15%. Rice Ili also noted that the fracture strength of the

samples was only about 69 MPa (10 ksi) and this was related to the

large grain size of the deposit. Although we did not carry out a

-54-

TABLE 9

Summary of results on bend bar specimens

Hardness Fracture TRSRun kg/mm2 toughness (3 point)

# (load) Kc, ramr MPa (ksi) REMARKS

168 2505 (200) 6.1 392 (57) HLM graphite substrate

170 2215 (500) 3.55 123 (18) RBSN substrate

173 4130 (100) - 197 (29) HI1 graphite substrate

175 3480 (300) 165 (24) HLM graphite substrate

1

-- II

1 -55

-0J

44K

'4441" V" 'Y"%j4

FIGURE 17 Morphology of SiN 4 deposit on bend bar specimens.

(A) 2000X

(B) 2000X

-56-

dk-tii led inves ti gat ion of the rel-t ionshi p be tween strength and the

sizt- of crystallites, our results generally support his findings.

(e) Measurements of electrical properties

As discussed in the experimental procedure (p. 3 ),this was

not a part of work scope of the pre-sent program. However, the results

art- included here since there is an interest in Si N,, as a dit-lectric

*1 material. The samples for these measurements were made under another

program. The evaluation was carried out elsewhere. Table 10 gives

daita for our material. We also include data for other silicon nitrides

a.ad a SiAlON for comparison.

-57

IV. SUMMARY AND CONCLUSIONS

The objective of the present program was to evaluate various

methods of refining the grain structure of CVD Si3N4 deposited

on an indirectly heated substrate. We examined various deposition

chemistries to influence the reaction between silicon and nitrogen.

Experiments were conducted to study the effects of nitrogen, argon,

SiF4 , propane, MTS and aluminum on the process parameters and

morphology of the deposits. We also studied the possibility of

depositing elemental silicon by the disproportionation of silicon

halides and its subsequent nitridation.

We found that in most chemical systems studied the tendency of

SIC1 4 (or SiF 4 ) to form intermediate species in the vapor phase

by reacting with NH3 caused difficulties in controlling the process

parameters. This reaction resulted in deposits having a variety of

crystal morphologies and properties. However, the simultaneous

presence of aluminum chloride and its reaction with ammonia resulted

in a non-columnar deposit of Si3N4-AlN. Thus, although the attempts

to apply the CNTD process for depositing non-columnar, fine-grained

Si 3N4 were largely unsuccessful, valuable understanding was gained

regarding the chemistry of SI3N4 deposition. The salient points were:

(A) The silicon halide-ammonia system is not amenable

to CNTD-type grain refinement due to the propensity for vapor phase

reaction and formation of non-volatile intermediates.

(B) Additions of carbon, either as MTS or as propane, do

not cause grain refinement in Si3Ni4 under the experimental conditions

used in the present work.

~-58-

(C) The codeposition of A1N with Si3N4 apparently

permits grain refinement. This is probably due to the competitive

nature of nitridation reactions for Al and Si. A non-columnar deposit

of AIN-Si 3N4 is obtained.

The mechanical properties of Si3N4 made by the indirect heating of

substrates were comparable to those obtained on directly heated substrates.

The flexure strength values were 205 MPa (29.8 ksi) ± 80 MPa (11.6 ksi),

with values as high as 450 MPa (65 ksi). The hardness of the deposits

was usually in the range HV 2500 to HV 3000, with values as high as

HV 4130 and as low as HV 1900. The indentation fracture toughness was

about 4.0 MPa/m, with values as high as 5.8 MPaVrm.

In conclusion, the present work clearly demonstrated the potential of

vapor deposited silicon nitride in terms of achievable properties.

The concept of codeposition of a second phase to minimize or eliminate

the columnar growth habit was shown to be feasible in the initial

experiments.

An advantage of the vapor deposition technique is the possibility of

studying very pure alloy systems. Conventional powder technology

is very often limited by the presence of impurities, intentional or

otherwise. Therefore, it should be noted that the vapor deposition

technology offers the possibility of studying Si-Al-N system without

Ai having to deal with oxygen. The initial success of the codeposition

1, work warrants further development work to refine the system and study

the feasibility of depositing a range of SiIN,,-AIN compositions for

high temperature applications.

-59-

0 C C

x x

E-~ Lt~ r'

144

0

C14

00

P.4 4

po Cz ~-o C

60-

REFERENCES

1. Holzl, R.A.:"Investigation of the CNTD Mechanism and Its Effecton Microstructure and Properties of Silicon nitride," Sunmmarv

Report, U.S. Naval Air Systems Connand Contract #N00019-77-C-0395.July, 1979.

2. Evans, A.G. and Charles, E.A.: J. Amer. Ceram. Soc., 57, 371(1976).

3. Holzl, R.A.:"Grain Refinement by Thermochemical Means," Proceedings

of 6th International Conference on Chemical Vapor Deposition, Atlanta,Georgia, The Electrochemical Society, Princeton, N.J., (1977),p. 107.

4. HoLzl, R.A.:"An Investigation of the CNTD Mechanism and Its Effect onMicrostrurtilral Properties," U.S. Air Force Office of ScientificResearch Contract #F49620-77-0086, March, 1977.

5. Stiglich, J.J., Bhat, D.C., and Holzl, R.A.: Ceramurgia International,6 (1), 3 (1980).

6. Dutta, S., Rice, R.W., Graham, H.C. and Mendiratta, M.G.: "Character-ization and Properties of Controlled Nucleation Thermochemical Deposited

(CNTD) Silicon Carbide," NASA Tech. Memo 79277, paper presented at 80th

Annual Meeting of American Ceramic Society, Detroit, Michigan, May, 1978.

7. Panos, R.M. and Bhat, D.G.: "An Investigation of the CNTD Mechanism and Its

Effect on Microstructural Properties." Interim Report, U.S. Air ForceOffice of Scientific Research, Contract #F49620-79-C-0041, March, 1980.

8. Gazzara, C.P. and Reed, D.: "A Computed X-ray Diffraction Powder Patternfor Alpha and Beta Silicon Nitride," AMMRC TN 75-4, Army Materials andMechanics Research Center, Watertown, Mass., April 1975.

9. Kijima, K., Setaka, N. and Tanaka, H.: J. Cryst. Growth, 24/25, 183(1974).

10. JANAF Thermochemical Tables, Second Edition June 1971.

11. Nihara, K. and Hirai, T.: J. Mater. Si., 12, 1243 (1977)

12. Wannagat, U.: "Advances in Inorganic Chemistry and Radiochemistry,Vol. 6, p. 225, Academic Press, New York (1964)

13. Lin, S. - S.: J. Electrochem. Soc., 125, 1877 (1978'.

14. Lin, S. - S.: J. Electrochem. Soc., 124, 1954 (1977).

15. Rochow, E. (;.: "The Chemistry of Silicon," Pergamon Texts in InorganicChemistry, vol. 9, p. 1340, Pergamon Press, New York (1973).

16. HolzI, R.A.: Unpublished work.

I -61 -

17. Seymore, W.C. and Byrne, J.G.: "The Influence of MoCi! on the

Chemical Vapor Deposition of Tungsten from WFb," Proceedings of5th International Conference on Chemical Vapor Deposition, England,p. 815 (1975)

18. Landingham, R.L. and Austin J.H.: J. Less Common Metals, 18229 (1969)

19. Rice, R.: Private Communication.

20. Thorp, J.S. and Sharif, R.I., J. Mater. Sci., 12, 2274 (1977)

21. Walton, J.D.: Amer. Ceram. Soc. Bull., 53, 255 (1974)

22. Popov, E.P.: "Introduction to Mechanics of Solids," p. 202, Prentice-Hall, Inc. Englewood Cliffs, N.J. (1968).

1

4t .+ , ++

APPENDIX 1: Deposition Conditions

for S13N4

-63-

TABLE A-I Deposition conditions for Si3N,?, made with nitrogenas carrier gas for the precursors

Total Substrate Run DepositionRun Gas Flow Rate, ml/min Pressure Temp. Time rate0 SICx. NH, H2 Nj Torr. OK min om/hr

1-1 30 150 400 2700 25 1635 30 781-2 30 150 400 2700 25 1575 30 78

1-3 30 150 400 2700 25 1500 30 7

1-4 30 150 400 2000 25 1500 30 -

1-5 30 150 400 4300 26 1650 30 48

1-6 30 150 400 8600 39 1650 30 48

1-7 30 150 400 11,550 52 1650 30 48

1-8 30 150 400 11,750 52 1650 120 66

1-9 30 150 400 11.750 48 1620 60 48

1-90 30 150 400 15,000 64 1650 60 36

1-11 30 150 400 15,000 60 1675 60 18

1-12 30 150 400 15,000 66 1735 90 60

1-13 30 150 400 2700 25 1635 180 66

1-14 30 150 400 8600 40 1650 180 102

1-15 30 150 400 11,550 52 1700 30 96

1-16 30 150 400 11,550 55 1650 30 24

1-17 30 150 400 11,550 62 1650 45 54

1-18 30 150 400 11,550 6 1700 45 36

1-19 30 150 400 11,550 58 1750 60 72

1-20 30 150 400 11,550 58 1800 60 -

1-21 30 150 400 6,550 59 1650 30

1-22 30 150 400 8600 45 1650 60 6

1-23 30 150 400 8600 47 1650 60 0

1-24 60 300 15,865 78 1650 30 ISO

1-25 37.5 187.5 500 8600 48 1650 60

1-29 250 87 975 2400 28 1525 120 8

1-35 30 150 400 8200 41 1645 90 48

1-36 30 150 400 8200 40 1645 90 9

1-37 30 150 1400 7200 42 1645 60 90

1-38 30 150 400 4100 40 1645 90 60

1-58 30 140 4400 3720 47 1650 60 36

1-59 30 150 4400 3720 47 1775 60 10

-64-

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-65-

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-66-

TABLE: A-4 Deposition condttions for the study of dtsproportlonatlon of silicon halide

Si

Total Reser voi r Subst rate Run Shtr~RUN Gas Fl, Rate, ml/rn Pressure Temp. Temp. Tine M.terlal.

# SIC;_ NIt, NZ _ _ Ar iillC e.___orr OK vr _d used

8-569 Soo 2 0 100 0 41 1975 1W25 10 UT- g' zraphi t9-573 275 O 0 0 2000 0 279 1950 I1115 11 VT- 2 2 tir pht, e

8-574 200 10 0 0 2000 0 290 1925 1300 30 UT-i2 grapiite

8-575 200 II0 125 0 2000 0 53 1975 118 30 L rT-2 ')t t

8-576 200 200 125 0 2000 0 58 1975 1273, P, 5 - 'aphl !

8-577 210 200 125 0 2000 0 60 1975 1425 (0 1- apI I t t,"

8-578 200 O 125 2000 0 0 60 1975 I - grapht I '

8-589 100 200 125 2000 0 0 5 1975 1435 4 ' -

8-'8C9 I,)0 2"() U 2200 0 0 55 1995 1R, .' 2I ,-ral t,.

8-"81 20 510 250 2200 0 0 57 1975 17 250-22 rt .]hlt

9-982 100 1600 0 2200 0 0 50 i975 L'T -22 y r apt, II

8-589 500 1 1) 2200 0 55 1675 1475 .10 -21 rahlte_

8-58S WOO 00 150 2000 0 0 42 1975 152 Pl 4'-'2 ;,. ap t t

8-58] 1O0 0 0 2200 0 0 37 1995 182, t',

1T-.2 g tC p oI

8-5A 7 10 5(50 250 2200 0 0 45 1 775 172S • '"-21 ral I,

8-58 200. 0 ( 2200 0 0 44 1975 16() 3, 11-22 gral'i t

•-,89 500 110 0 50 1925 112 IC- 22 - 6.erl ,.

"-"9 1OO 0 0 n 1200 0 40 1975 15', 60 LO- 7 r.- t',N,

-- 591 100 0 0 2200 0 0 45 1900 162'. 20 T-'2 , ap, i r

R-,92 IO0 510 0 2200 0 0 45 -,O0 161 ( 1'T-22. a, ih PON

P-191 IO0 5'0 J ) 2200 0 0 47 1500 1821 0 Vc- I r*'hI'

9-594 100 500 ( 2200 0 0 45 1810 IS NC- 3% S I rIC

8- 5 1300 Soo o 2200 0 0 43 1 180 60 NC-1 ,0 ,AI.F.ai'l l '"9~ -119F) Io 500 0 2200 o o 45 17 7', 30 NC:-,. I'- I t, .... 1,. ,IM,'-.,- 597 I90o 5(30 £) 2200 0 0 4S5 17 80 V, tl-2Naa FF %

-5198 100 5110 0 2200 0 0 46 1925 1810 W NC,- 3-.. rji.,IIC

8-99 I00 500 ( 2200 0 0 45 1910 181C is NC- 350, grav hit-'

8- " 100 2100 2 2200 0 0 S8 190 181 30 NC- I),. Riaph.IC

9-,101 100 1 20 400 0 584 1900 1800 t) NC- 3,:. rTC 1,"

8-605 300 1500 0 2200 0 0 50 1925 182,. 30 - 3.P, J ,T -

A-606 3 00 200 400 0 0 584 1900 1700 10 NG- 3%0, 25!ral;t,

8-604 00 0 -4 0 400 1 0 5 4 1925 1700 (40 NC-350 ,: iA- 'V 0 I ()I O) 600 400 0 O 590 1875 16". 30 ,p t

8-696 200 O 1200 400 1 0 597 192 170 215 Rap l

R6-5)9 50O U 1400 0 1000 0 40 1675 40 iraphLt'

851[1 500 ) 0, 0o 0 1 000 0 483 1675 40 1r lt,IIC

8-61 Soo 0 10,000 1500) 0 0 483 - 1700 I0 Arar,'lte

A-612 500 o 0000 5000 O 0 481 1710 30 rh te

8-563 5o 100 I0.000 53Oo 0 ( 483 171n 30

8-NI'., 500 0 200] 10,000 0 0 483 1875 30 gYapbU1

' , 'drod

9-61' S(1O 0 10,000 9000 0 0 457 1695 187 lT-22, N N0 I A"591

8'7 mla. t;I d.v- I Ir"3 hr. ntrl)d-tF v4

16000 . , . ,,w

9-Ni 0 0-1000 0 s5000 O 500 50 1550 1625 35 'T-22 Rr,-phlte

9-617 0 2)0 ' n 5O10 0 600 4(0 1525 1655 4' IT-22 Rraphlt

8-618 0 200 0 7)00 It 500 50 1475 I,50-1525 20 ITT- 22 Eraphl te

NOTES Il) The firt 12 runs tip to 8-583 were cond.cted under 1FOSR gr ta within the scope of a %imilar InvestIRatlIonin the SIC dep,Iltion.

(2) In all runt eOx',pt the liat I (i.e. 61its, 681. ), 13N1 %trap wast oed in the reservoir.

67

Oc.- P4j 93 00 o - IT CD

0 0D CDt -.* 0~ r- 0D 'D '

U)W -i -4 4-4 -4 1 - -4

cz W

w ~ ~ " 0 'i 0 '0 C0 '0 0 CD '0 r-0. CE-4 . , , ,

CC

C~~ 0 -. ' 0 0 0D 0Dm C l) c -Tj c, n m' w a'

(7 TO 11 C14

4-o 04 C 0 0) 0l 01 0 0 0) 0W- C ~-s~j CN -4 -.5 T

'4-. 0

-4

n Cn ,-4 111 Lfn Ltl Lf-4 -44 -4

0

. 4

4-)

I

0D -4 N1 C . L~' r, 0Lf.r Lfn L~ f Lr Lf-) U.U- LI') 'D

V I I I I I I I I I-4 -4 -4 - 4 4 -- 1 1-4 1-4

0

-4

41

E-400 1- 4 1-

U)

0

0)

CO J

E-44 ,4 -

-q

-l 0

J-O0 0 0 0 0

.1 ))D C

0 0400 0) C)

4~- -N '.

'4

'-4 ~ 010

0 E

CD C) NDc)cD) I -n c 0n

C) C) C-) C) C0 (D C) ) D C) CD'e, m- m Lt n n C) mn tn tn mn tn

(:0. 0 L-) C) -n c) c) u) 0n Ln C C) -nf" U) u') c) cfl c) ri Ifo ILr tn Lfl ") o

-1 ~CA-J C' C. N N ND G)N N

41

0 )

-H C)

r-( c) c c D0 r n c )

C)) (Nc) r U ) 'CP CN ) C) -)0) 0C4 > N N: C) C) C) C: NC

C)

C ~ ~ 0 0) C ) C ) ( C). C) C) CD

4- 0 CD4 0 C, 0 C) C ( C) C) m)

U) I - -A N I I N (N4 (N N (N (N (N0

U)N

HC) C) C) CD (D ) C) C) C) C) C) C)

o C C) ) C) C) C C) CD CD (D (D C)

co m m m co CO c c-i mX m m m m

I -4

'7 '

r r -f

:-C1 ar.10: a a

CDI

:k- Or 0c o- c 'J cc c c

C, i_ c _ __ __ __ _

APPENDIX II: Calculation of transverse rupture strength of a coated beam

The calculation of the transverse rupture strength of a simple beam is

accomplished by means of the flexure formula. When the beam is

composed of different materials, having different elastic moduli, the

calculations can be made by mathematically converting the composite

beam to that made of any of the constituent materials comprising the

original beam. Thus, when it is of interest to determine the strength

of the coating of material A on a bar of material B, the composite beam

is converted to a beam of material A by the method of equivalent

sections!22) In this method the cross section of the substrate (B) is

replaced by an equivalent section of the coating such that at a given

magnitude of axial strain, the forces developed in the substrate and

the equivalent section of the coating are equal. Then the entire

section can be treated as a single homogeneous material. The

equivalent section is generated by changing the dimension of the substrate

in the direction parallel to the neutral plane.

For a given axial strain e, the force developed on the substrate is

F = e.E .A . At the same point in the coating, the force is

F = e.E .A . For F = F , we have E .A = .A = nE A wherec C c s c c c S s c s

n = E /E • Thus the area of cross section of the coating to replaceS c

an equivalent area of the substrate is n.A s

For a bend bar of rectangular cross section as shown in Fiure A-I

the area of the substrate (A, = b. h.,) is transformed into an equivalent

area of the coating bv changing b, to n.b . Thton, the moment of inertia

-71-

1b

v-MATERIAL A

b2b

MATERIAL B

MATERIAL A

2 2*1 #1 - -(n .b , 2 t~

h 2 2

FIU'RE A-] METHOD~JI OF EOUI VALENT SEiCT ION

-72-

P

KA L/_

p/2 P,2

(a) 3 -point flexure

P/2 P,

(b) 4 -pointflxr

Fig. A 2 Loading configurations in flexure tests

-73-

of the equivalent cross section which becomes an "I" beam, is given by

bjh1 3 - (I-n) b2hz)12

Then, for a three point flexure (center-point loading) test (Figure A-2)

3P lh 1TRS - 2{blh1 - (1-n) b';,h23 }

It is assumed in the above equation that the failure occurs in the center

of the span. When the failure occurs elsewhere, the flexure formula is

modified to

TRS 3Ph (1- 2x)

2jblh, - (1-n) bh,

Where x is the distance between the central loading pin and the point of

fracture. The expression for the four-point flexure test is

TRS (4-point) = b h- (-n) b 2 h 23

where a can be /3 (1/3 - four point) or Z/4 (1/4 - four point), as shown

in Figure A-2,

-

i~i'.-74-

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